Human immunodeficiency virus (HIV), the etiologic agent of the acquired immunodeficiency syndrome (AIDS), is capable of killing cells which express the CD4 cell surface protein. The cytopathogenic ability of HIV accounts, in part, for the severe immunosuppression associated with AIDS and may underlay other pathological features of this devastating disease syndrome. HIV infection of H9 cells, a CD4+ lymphoid cell, results in cell swelling which culminates in cytolysis. Preliminary studies have demonstrated that an increase in intracellular monovalent cation levels occurs at an early time during the acute cytopathic phase of HIV infection, and that these alterations in ion content are due, in part, to an inhibition of the plasma-membrane-associated Na+/K+ ATPase. Ion transport systems which regulate the intracellular levels of monovalent ions, such as the Na+/K+ ATPase, have well-characterized roles in cell volume control. Therefore, inhibition of the Na+/K+ ATPase may mediate the loss of volume regulation induced by HIV. The mechanism by which HIV alters the activity of the Na+/K+ ATPase will be elucidated by kinetic analysis of 86Rb+ uptake and by binding of (3H) ouabain in intact cells. Activities of the Na+/K+ ATPase will be quantitated in permeabilized cells and in isolated membrane preparations. The roles of intracellular nucleotides, membrane potential (delta psi), intracellular pH (pHi), (Ca++)i and membrane lipid composition in the HIV-mediated inhibition of the Na+/K+ ATPase will also be investigated. Expression of viral proteins or of CD4+ will be examined in parallel with alterations in membrane-associated transport systems by "two-color" flow cytometry employing fluorescent probes and monoclonal antibodies to the HIV envelope proteins. Elucidating the mechanisms by which HIV disrupts cell volume homeostasis may lead to strategies of interfering with the cell killing processes or to an understanding of the mechanisms by which some cells survive HIV cytopathology to establish chronically-infected cells. The proposed work will also provide a foundation for a rational approach to the development of antiviral agents which are selective for HIV-infected cells.